1. Field of the Invention
The present invention relates to a mobile communications system, a mobile communications method, a server, a transfer device, and a mobile communications terminal for supporting moving networks.
2. Description of the Related Art
A mobile communications system employing a Global v6 routing scheme is conventionally known as a mobile communications system for supporting moving networks. A mobile communications system employing a Hierarchical Mobile IP (HMIP) is also conventionally known as a mobile communications system for supporting moving networks.
In the mobile communications system employing the conventional Global v6 routing scheme, when a moving network is performing a handoff process, it is necessary to notify home agents of all mobile communications terminals within the moving network, of the movement. In the mobile communications system, it is also necessary to notify terminals as correspondent nodes of the movement, so as to implement route optimization during the handoff process of the moving network.
As a result, the mobile communications system causes increases in the amount of signals to be transmitted and handoff processing time during the handoff process of the moving network.
Specifically, as shown in FIG. 1, in the mobile communications system, when a moving network A moves, that is, when the connection to an access node AN to which the moving network A is connected is changed to another access node, address information of all mobile terminals (mobile communications terminals) MT #1 and MT #2 located in the moving network A is changed. Hereinafter, the address information of the mobile terminal is called the mobile terminal address information.
In the example of FIG. 1, a connecting node of the moving network A is changed from AN 1 to AN 2, and mobile terminal MT #1 address information (Care-of-Address [CoA]) is changed from “AN1prefix+#1” to “AN2prefix+#1,” and mobile terminal MT #2 address information (CoA) is changed from “AN1prefix+#2” to “AN2prefix+#4.”
At that time, in the mobile communications system, home agents HA 1 and HA 2 of the mobile terminals MT #1 and MT #2 and mobile terminals MT #3 and MT #4 as correspondent nodes are notified of the changed mobile terminal address information, thereby to be able to continue communication without breaking an optimized communication route.
In the mobile communications system, however, it is necessary to notify all home agents and correspondent nodes of the movement of the moving network A, requiring a large amount of signals and much processing time before the completion of update of the mobile communications terminal address information, and causing difficulty in supporting real time communication.
The mobile communications system performs Duplicate Address Detection (DAD) to prevent the address information (CoAs) on the mobile terminals MT #1 and #2 from being the same as that on other mobile terminals. There is thus a possibility that a portion following “AN1prefix” (e.g., #2) will be changed in a CoA newly provided when the moving network moves, causing an increase in time required for the update of the mobile communications terminal address information.
A mobile communications system employing the conventional HMIP, in which, instead of all home agents and correspondent nodes, a Mobility Anchor Point (MAP) is notified of the movement of a moving network, is thus superior to the above-described mobile communications system employing the Global v6 routing scheme.
In this mobile communications system, however, it is also required to update address information of all mobile communications terminals located in a moving network when the moving network moves, preventing a substantial reduction in handoff processing time.
Specifically, as shown in FIG. 2, in the mobile communications system, when a moving network A moves, that is, the connection to an access node AN to which a mobile node MN configured to manage the moving network A is connected is changed to another access node, address information of all mobile terminals (mobile communications terminals) MT #1 and MT #2 located in the moving network A is changed.
In the mobile communications system, the MAP placed in a core network 1 holds pieces of next hop destination information (CoA_MN) for transmission to all the mobile terminals MT #1 and MT #2 located in the moving network A, which information pieces are not correlated. It is thus required to transmit to the MAP individual update information on all the mobile terminals MT #1 and #2 located in the moving network A when the mobile terminal A moves, causing an increase in handoff processing time.